fdo#83302 don't display read-only infobar for Base form in normal mode

Change-Id: I6faae7f5b1b2ec243c53453a8627bd0a540a46ad
Reviewed-on: https://gerrit.libreoffice.org/11219
Reviewed-by: Bosdonnat Cedric <cedric.bosdonnat@free.fr>
Tested-by: Bosdonnat Cedric <cedric.bosdonnat@free.fr>